Membranes, close meshed thick

Close meshed membranes. Only ions or molecules up to a certain size can pass the membrane. They work similarly to those which are thick with respect to adjacent mixed phases but they are able to host certain ions or molecules and, at least in principle, may transport them from the side of higher electrochemical potential to the side of lower electrochemical potential. Such membranes are named semipermeable. Here, an electric potential difference between the two solutions exists, which is called Donnan potential. 

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